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Audio 101 Part Ten: Analog III

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Written by Colin Smith

Created: 01 June 2011

Owning the finest record player on the planet won’t do a vinyl aficionado a bit of good if he doesn’t have a phono preamplifier. But what is a preamplifier, and why is there a special kind of preamp for record players?

Back in Audio 101 Part Four, I said, "Basically, a preamp provides an intermediate stage between the low-level signal output of a source device and the relatively high level an amplifier prefers at its inputs. For completeness, a phono preamplifier will comprise a number of gain stages to boost the very-low-level electrical signals generated by a phono cartridge into something that even a preamp can work with." In other words, because a cartridge gives a preamplifier less to work with, electrically speaking, a phono preamp must boost the signal a lot more than a regular preamp would just to bring the phono signal to the same level as, for example, the relatively high-level signal output by a CD player.

There are different phono preamps to work with the two main types of cartridge, moving-magnet (MM) and moving-coil (MC). These days, most phono preamps contain MM and MC sections in the same box -- though not always, and probably not at the lower end of the price spectrum. One relatively low-priced phono preamp with both MM and MC sections is Clearaudio’s Smart ($600 USD). Let’s take a look at how it manages these signals.

A quick look at the Smart’s spec sheet reveals that its electronics provide a boost 50% greater (60dB vs. 40dB) for MC cartridges than for MM. As I explained last month, while an MM cartridge’s output signal strength is low, MC cartridges make MMs look like Hercules himself -- MC signals require a great deal more preamplification to get them up to line-level standards.

Last month I wrote about how external vibrations can be picked up by the stylus and interfere with the intentional vibrations created by the stylus moving through the record's grooves. By the same token, phono preamps must be carefully designed to ensure that their own electrical noise is at a level low enough that it won’t interfere with the incoming signal. If electrical line noise, for example, were to burrow its way into the audio signal from the turntable, it’s easy to imagine that that noise would be hugely amplified by the phono preamp and damage the audio signal. The Clearaudio Smart’s claimed ratio of signal to noise is 65dB; i.e., the component’s self-noise threshold is 65dB below the specified level of the audio signal. While that’s pretty amazing, more costly phono preamps can have noise levels far, far lower.

Because a phono preamp’s job is to boost the cartridge’s signal to a point where it is more or less equal to what a CD player can output, a phono preamp’s output must still be fed into a preamplifier -- which is why very few standalone phono preamps come with a volume control. A component equipped with its own internal phono stage -- whether a standalone preamp, integrated amplifier, or receiver -- still must pass the phono signals amplified by that stage to another preamplification stage before it can be boosted by the power amplifier into something the speakers can use.

I’ve often written that the biggest problem with CD players is the medium they play. Similarly, the biggest hurdle turntables face is that they depend on vinyl records that are made more or less as their ancestors have been for over a century. If a CD can leave the manufacturing plant with its center hole offset a bit and/or not perfectly round, it’s easy to imagine the kinds of flaws that can haunt a vinyl record. Even when modern technology has been applied to the manufacture of top-flight audiophile records, they’re still made of a material that is less than robust and doesn’t like temperature fluctuations: cold vinyl is brittle, and warm vinyl will pull a Salvador Dalí on you faster than you can say, "Is it just me, or is this record turning into a taco shell?"

Rejoice, vinyl fans -- for every inherent flaw in the design of the long-playing record, there is an accessory designed to mitigate the damage. Here is a list of a few of them:

Record clamps

These are designed to do as their name implies: clamp the record to the platter. A perfectly flat record is far easier for the stylus to track than one whose center section resembles Mount Fuji. Of course, an inherent problem with record clamps is that they can directly clamp only the label section at the center of the record, leaving unclamped the entire grooved, signal-bearing surface. This obviously limits how flat a record can be made to be. To address this, some high-end turntables have a platter fitted with thousands of tiny holes through which a vacuum pump sucks air, to keep the entire surface of the LP flattened against the platter.

Record presses

If a six-figure turntable isn’t in your future, then the next-best way to flatten your LPs is in a record press. The one I see most commonly at audio shows, the Furutech DF-2 LP Flattener ($2387), takes one to two hours to slowly heat a record to 149°F, press it flat, then slowly cool it down to room temperature.

Record destaticizers and demagnetizers

Anyone who’s ever worn polyester knows that it generates static electricity as Wall Street generates Ferrari owners. Vinyl, chemically similar to polyester, is also heavily affected by static electricity, and some accessory makers would have us believe that static electricity is as bad for sound as American Idol is for music. They offer antistatic technology in many forms: the Milty ZeroStat gun ($100), the AudioQuest electricity-conducting carbon-fiber brush ($29), and Furutech’s flying-saucer-like DeMag LP Demagnetizer ($2448), which is also a destaticizer.

Record-cleaning machines and stylus cleaners

Hands up if you knew that these machines exist. While many of us got by with an Audio-Technica record brush that looked to be made of corduroy and some secret-sauce record-cleaning fluid, our high-end cohorts were using the thermonuclear device of record cleaning: the record-cleaning machine (RCM). There seem to be two types of RCM: one that works a lot like a turntable, and one that attaches to a record as a parking boot does to the wheel of a naughtily parked car, and rotates the record in the vertical plane.

In the turntable-like record cleaner, a brush and vacuum take the places of the stylus and cartridge. The vacuum captures cleaning solution that is injected onto the record at the start of the squirt-brush-suck sequence, much like a carpet steam cleaner (minus the steam). Record-cleaning machines of this sort tend to cost from $350 to $4000. On the other hand, the vertical-plane Spin-Clean ($79.99) works by rotating both sides of a record through a bath and a brush. The downside is that LPs must then be dried by hand; the Spin-Clean has no grime-sucking vacuum system.

Compared to RCMs, stylus cleaners are altogether more reasonably priced. The most expensive I could find at the home of all things vinyl, Jerry Raskin’s Needle Doctor, costs a mere $69.99. Simple stylus-cleaning brushes cost as little as $3, while more advanced ones, including cleaning solution, come in at less than a family trip to a burger joint.

Turntable mats

A turntable mat goes between a turntable’s platter and the LP. The most basic type is the good old felt pad, which is a horrible substitute for, oh, I don’t know, air between platter and record. Better are mats designed to improve sound quality. The Funk Firm’s Achromat Universal record mat ($90-$100, depending on thickness) is claimed to be like a vinyl record, but it’s full of damping air bubbles that, the company says, will cause you to hear "more space and air, inky black backgrounds, layered timbral color, better midband resolution, and a more sonorous, deep bass." Other mats float the record on pads so that it never touches the platter (see, in contrast, megabuck vacuum-hold-down systems are designed to effectively glue the record to the platter), while some cheapie mats are just the plain old antistatic variety.

Tune-up supplies

While the merits of some of the devices listed above are debatable, every vinyl fan must own a minimum of tune-up tools if he or she wants to be sure a turntable is giving all it can give. Cartridge- and stylus-alignment tools are must-haves -- misalignment is as bad for sound quality as it is for steering a car. Alignment tools don’t have to be expensive (alignment charts can be found for free on the Internet), but will make a huge difference in a system that hasn’t been set up to perform at its best.

A plethora of other accessories are available, but they’re of more universal application -- think footers, equipment racks, and power conditioning. I’ll get to those a little further down the road. Next month, I’ll write about cables. Now, where did I put my hard hat . . . ?